Answering mails on a weekend is a good thing - unless you send the mails.
If you feel like it, it’s no problem to get your inbox cleaned on a weekend because there is nothing more liberating than facing an empty inbox on a monday morning. You just need to schedule the answers to be sent on the next work day earliest.
Nobody expects to get an answer between Friday 5pm and Monday 9am and you should not break with this convention.
Whilst it may look nice to your customer, it won’t feel that professional. Someone might get the impression that your product is a pet project of yours and you are tinkering it in your spare time. Even if this is your hobby - wait until Monday.